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P0374 Code: Timing Reference High-Resolution Signal “A” No Pulses

P0374 means the PCM detected no pulses from high-resolution timing-reference Signal “A.” Learn the symptoms, causes, testing process and repair costs.

The P0374 code means the powertrain control module is receiving no pulses from timing-reference high-resolution Signal “A.”

This is not merely a weak or occasionally unstable signal. The PCM expects a repeating pulse train but sees none. Depending on the vehicle, the missing signal may prevent the engine from starting, cause it to stall or force the PCM into a reduced-power strategy.

P0374 is frequently associated with electronically controlled diesel injection systems that use an optical sensor and slotted encoder disc. However, its exact application varies by manufacturer. Check the wiring diagram and service information for the specific vehicle before replacing anything expensive.

P0374 Quick Reference

ItemDetails
CodeP0374
DefinitionTiming Reference High-Resolution Signal “A” No Pulses
SystemEngine-position or fuel-injection timing reference
Primary faultComplete absence of Signal “A” pulses
Common causesFailed sensor, open circuit, missing power or ground, blocked optical path or damaged encoder
Common symptomsNo-start, stalling, extended cranking or reduced power
SeveritySerious
Safe to drive?Generally not recommended
Best diagnostic toolScan tool, multimeter and oscilloscope

You can find additional definitions in the complete P-series OBD-II code list or browse the Pro Street OBD-II Doctor.

What Does the P0374 Code Mean?

P0374 is stored when the PCM does not detect any high-resolution pulses from timing-reference Signal “A” during a period when those pulses should be present.

Depending on the engine and manufacturer, Signal “A” may come from:

The PCM uses the signal to determine precise engine or injection-pump position. If the pulse train disappears completely, the PCM may lose the information required to control fuel delivery, injection timing or ignition timing.

The “A” designation identifies a particular timing-reference circuit. It does not automatically identify Bank 1, Sensor 1 or one universal component location.

How High-Resolution Signal “A” Works

A common version of this system uses an optical sensor and a rotating encoder disc inside an electronically controlled diesel injection pump.

The encoder disc contains precisely spaced slots. As the disc rotates, the slots allow light from an internal source to reach the optical sensor. Each transition generates an electrical pulse.

Other applications use a Hall-effect or magnetic sensor reading a toothed reluctor wheel. The hardware differs, but the PCM still expects a repeating signal that corresponds with engine rotation.

A functioning high-resolution signal allows the PCM to calculate:

A normal oscilloscope waveform displays a repeating pulse pattern with predictable amplitude and spacing. A P0374 waveform remains flat because no pulses reach the PCM.

Common Symptoms of P0374

Symptoms depend on whether the PCM can use another position sensor as a substitute.

Common P0374 symptoms include:

Some vehicles may continue running by relying on a lower-resolution position signal. Others will not start without the high-resolution timing input.

Common Causes of the P0374 Code

Possible causes include:

A completely flat signal often points toward a basic failure such as missing power, missing ground, an open signal circuit or a dead sensor. That does not mean the sensor should automatically be replaced. The wiring still deserves an inspection before the parts cannon gets loaded.

How Serious Is the P0374 Code?

P0374 is a serious fault because the PCM has lost a timing-reference signal it expects to receive.

The vehicle may:

If the engine stalls, misfires heavily or loses power, stop driving and arrange for proper diagnosis. A vehicle that can shut off unexpectedly is not something to casually monitor for another three weeks.

P0374 Compared With Related Codes

The P0370–P0374 family describes different failures involving high-resolution Signal “A.”

CodeMeaningDiagnostic focus
P0370Signal “A” MalfunctionGeneral circuit or signal fault
P0371Signal “A” Too Many PulsesExcessive pulse count or false transitions
P0372Signal “A” Too Few PulsesPulse count below the expected value
P0373Signal “A” Intermittent/Erratic PulsesSignal appears, disappears or becomes unstable
P0374Signal “A” No PulsesComplete absence of the high-resolution pulse train

P0374 owns the complete no-pulse condition. It should not be used as another general timing-sensor article.

P0374 Versus P0322

P0322 means the PCM is not receiving a signal from the ignition or distributor engine-speed input circuit.

P0374 is more specific. It identifies the complete absence of pulses from high-resolution timing-reference Signal “A.”

The two circuits may be related on certain applications, but they should not be treated as interchangeable codes.

P0374 Versus P0335

P0335 identifies a malfunction in the crankshaft position Sensor “A” circuit.

P0374 identifies the absence of high-resolution Signal “A” pulses. That signal may come from an optical injection-pump sensor, distributor, crankshaft sensor or another timing-reference component.

Always identify the actual signal source using the manufacturer’s wiring diagram.

How to Diagnose the P0374 Code

1. Scan All Modules and Record the Codes

Connect a capable scan tool and record:

Do not clear the codes before recording this information.

Related crankshaft, camshaft, low-voltage or module-communication codes may reveal that P0374 is part of a larger power-supply or synchronization problem.

2. Verify the Engine Is Actually Turning

Before chasing an electrical fault, confirm that the component generating the timing signal is physically rotating.

Depending on the application, inspect:

A stationary encoder cannot generate pulses. Sometimes the sensor is innocent because the mechanical component it watches has stopped moving.

If the engine cranks unusually fast or has no compression rhythm, inspect the mechanical timing system before continuing with electrical tests.

3. Identify the Correct Signal “A” Circuit

Consult the correct wiring diagram and service information.

Determine:

Do not assume every P0374 application uses the same injection-pump sensor. Generic code definitions describe the fault, not the exact underhood layout.

4. Inspect the Sensor Connector

Disconnect the sensor connector and inspect it carefully.

Look for:

Reconnect the plug and make sure it locks securely. A connector that looks connected but does not fully seat can eliminate the signal entirely.

5. Inspect the Wiring Harness

Trace the circuit between the sensor and PCM or control module.

Check for:

Pay special attention to sections exposed to vibration, heat or recent engine repairs.

6. Check Battery and Cranking Voltage

Low cranking voltage can prevent the sensor, injection-pump electronics or PCM from operating correctly.

Test:

Compare the measurements with manufacturer specifications. If voltage collapses while cranking, repair the starting-system problem before continuing.

7. Verify Sensor Power and Ground

Turn the ignition on and back-probe the sensor connector according to the wiring diagram.

Check for:

A sensor cannot create pulses if it has no power or ground. Revolutionary stuff, admittedly, but this simple test prevents plenty of unnecessary sensor replacements.

Do not apply outside voltage to a signal circuit unless the manufacturer’s procedure specifically directs it.

8. Check Signal-Circuit Continuity

With the circuit powered down and the appropriate modules disconnected, test continuity between the sensor signal terminal and PCM terminal.

Also check the signal wire for:

Do not rely solely on an unloaded continuity test. A damaged wire may carry a meter’s tiny test current but fail under actual operating conditions.

Where appropriate, use a loaded-circuit test or voltage-drop measurement.

9. Test the Sensor Output

Reconnect the circuit and observe the sensor output while cranking the engine.

The correct testing method depends on sensor type:

Compare the measured output with manufacturer specifications.

If power and ground are correct but no signal leaves the sensor, the sensor or the component it reads may have failed.

10. Examine the Signal With an Oscilloscope

An oscilloscope provides the clearest evidence of a P0374 fault.

A normal signal should show:

A true P0374 condition shows:

Check the waveform at both the sensor and PCM.

If pulses exist at the sensor but not at the PCM, the harness or connector is faulty.

If no pulses exist directly at the sensor despite correct power and ground, inspect the sensor, air gap, encoder and associated mechanical components.

11. Inspect the Optical Path, Encoder or Reluctor

If the circuit checks correctly, inspect the hardware used to generate the pulses.

Possible problems include:

An optical sensor cannot produce a signal if light never reaches it. Likewise, a magnetic sensor cannot produce a usable waveform if the reluctor is missing, stationary or too far away.

12. Test the Injection-Pump Electronics

On affected diesel engines, Signal “A” may originate inside the electronically controlled injection pump.

If external wiring, sensor power, ground and mechanical operation are correct, the fault may involve:

Follow the manufacturer’s diagnostic process before replacing the complete pump. Some components may be serviceable separately, while other applications require pump replacement or professional rebuilding.

13. Evaluate the PCM Last

PCM failure is possible, but it should be considered only after verifying:

A PCM should not be replaced merely because it occupies the expensive end of the diagnostic flowchart.

Common P0374 Diagnostic Mistakes

Replacing the Sensor Before Checking Power and Ground

A new sensor will not generate pulses if the original problem is a missing voltage supply or failed ground.

Confusing a Flat Multimeter Reading With Proof of Failure

Some digital sensor signals switch too quickly for a basic meter to display clearly. Use an oscilloscope or frequency-capable meter when the service procedure requires one.

Ignoring Mechanical Rotation

A sensor cannot detect a reluctor, encoder or distributor shaft that is not moving. Verify mechanical operation before condemning the electrical circuit.

Replacing the Injection Pump Too Early

An open wire, weak terminal or missing ground can imitate an internal injection-pump failure. Complete circuit testing first.

Ignoring Cranking Voltage

Low voltage may disable sensor electronics or prevent the PCM from processing the signal correctly.

Treating P0374 Like P0373

P0373 indicates intermittent or erratic pulses. P0374 indicates that no pulses are detected. One waveform drops out; the other never gets invited to the party.

Skipping the Sensor-to-PCM Waveform Comparison

A valid waveform at the sensor but a flat line at the PCM proves the problem lies between them. That single comparison can prevent hours of guessing.

Common P0374 Repairs

Depending on the test results, repairs may include:

If the PCM loses learned crankshaft-position data after repairs, consult the P0315 crankshaft position variation relearn guide.

Estimated P0374 Repair Costs

Actual costs depend on component location, engine design and labor rates.

RepairEstimated cost
Diagnostic testing$100–$250
Connector or minor wiring repair$100–$400
Battery or ground-cable repair$100–$500
Timing-reference sensor replacement$180–$700
Crankshaft position sensor replacement$180–$550
Encoder or reluctor repair$350–$1,300
Injection-pump wiring or electronics repair$500–$1,800
Injection-pump replacement$1,000–$4,000+
PCM software update$100–$300
PCM replacement and programming$700–$2,000+

These are general estimates rather than quotes. On some diesel engines, accessing the internal timing sensor requires specialized equipment or major injection-pump work.

Can You Drive With a P0374 Code?

Driving with P0374 is generally not recommended.

A vehicle that still runs may be relying on another position input or backup strategy. It can still stall or lose power if synchronization deteriorates.

Do not drive if the vehicle:

If the engine will not start, avoid repeatedly cranking it until the battery is depleted. Repeated cranking only creates another problem to diagnose, because apparently one was not enough.

How to Verify the P0374 Repair

After completing the repair:

  1. Clear stored and pending codes.
  2. Confirm the battery is fully charged.
  3. Start or crank the engine while monitoring Signal “A.”
  4. Verify that the scan tool displays engine RPM.
  5. Observe the waveform at idle.
  6. Confirm pulse frequency increases smoothly with engine speed.
  7. Allow the engine to reach operating temperature.
  8. Perform a controlled road test.
  9. Rescan for pending codes.
  10. Complete any required relearn procedure.

A successful repair produces a stable, repeating waveform at both the sensor and PCM. Simply clearing the code does not repair the circuit, despite what some marketplace scan-tool descriptions seem to suggest.

P0374 Frequently Asked Questions

What does the P0374 code mean?

P0374 means the PCM detected no pulses from timing-reference high-resolution Signal “A.”

What commonly causes P0374?

Common causes include a failed sensor, open circuit, missing sensor power or ground, disconnected connector, contaminated optical path, damaged encoder disc or failed injection-pump electronics.

Can P0374 prevent an engine from starting?

Yes. If the PCM requires Signal “A” to synchronize ignition or fuel injection, the engine may crank without starting.

Can a weak battery cause P0374?

Yes. Low cranking voltage can prevent the sensor or control electronics from operating correctly. Battery voltage should be tested before replacing timing components.

Is P0374 always an injection-pump problem?

No. The code may result from external wiring, connector damage, a failed sensor, incorrect air gap, damaged encoder hardware, low voltage or PCM problems.

Is P0374 the same as a crankshaft position sensor code?

No. The signal may originate from a crankshaft sensor on some vehicles, but other applications use an optical injection-pump sensor, distributor pickup or separate timing-reference sensor.

What is the difference between P0373 and P0374?

P0373 means the timing pulses are intermittent or erratic. P0374 means no high-resolution Signal “A” pulses are detected.

How do you test for P0374?

Verify mechanical rotation, sensor power and ground, circuit continuity and sensor output. Use an oscilloscope to determine whether pulses exist at the sensor and PCM.

Do I need an oscilloscope to diagnose P0374?

An oscilloscope is strongly recommended. It confirms whether the signal is truly flat and helps determine whether pulses disappear at the sensor or somewhere in the wiring.

Final Thoughts

The P0374 code identifies a complete loss of high-resolution timing-reference Signal “A” pulses. The engine controller is not seeing the pulse train it needs for precise position and timing calculations.

Start with the fundamentals: confirm the engine and encoder are turning, verify battery voltage, inspect the connector and check sensor power and ground. Then compare the waveform at the sensor and PCM before replacing major components.

A flat waveform is useful evidence. It tells you the signal is absent; proper circuit testing tells you why.

For more diagnostic coverage, visit the Pro Street OBD-II Doctor and the complete P-series OBD-II code index.

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